1. Field of Invention
The present invention relates to the melting of scrap metal and more particularly to the controlled removal of coatings, such as lacquers, including epoxies, vinyls and acrylics, as well as oils, grease and other volatilizable and combustible surface contaminants on scrap metal as a prelude to, or in association with melting, but without adversely affecting the melting operation itself.
2. Description of the Prior Art
It is well known that coatings, such as lacquers, and other surface contaminants on aluminum can scrap and the like should be removed prior to melting in order to avoid unacceptable melt loss. One preliminary cleaning process typically employs an organic solvent such as acetone which removes a substantial portion of the lacquer, oils and other surface contaminants. The most common preliminary cleaning approach, however, is the delacquering furnace in which the material is continuously conveyed through controlled zones of increasing temperature, progressively heating the material to about 1000.degree. F. which volatilizes the impurities to effect their removal. After the scrap is held in the furnace for sufficient dwell time, the scrap eventually exits the furnace with very little remaining lacquer residue. For aluminum can scrap, the current delacquering process significantly adds to the cost of a pound of recycled aluminum. Additionally, the delacquering furnaces are a continual maintenance problem resulting in excessive downtime and costly delays for necessary repair. For example, if the temperature in the delacquering furnace exceeds about 1050.degree. F., the surface contaminants may ignite and cause a harmful fire to spread throughout the furnace. Thus, careful control is often needed to prevent these problems which, in turn, adds to the cost of recycling aluminum.
The prior art of melting scrap, also teaches that charged scrap metal must be submerged or immersed rapidly into a bath of molten metal to avoid oxidation and to minimize skim formation on the melt. In the method of the present invention, however, the charged scrap metal is deposited on a molten metal surface where it remains unsubmerged for controlled delacquering and deoiling to occur, without experiencing the adverse effects caused by oxidation of the scrap. Such adverse effects are avoided in the present invention because the substantial source of heat in the area where the scrap is deposited on the molten surface is from the molten metal.
Accordingly, an economical and effective method of removing coatings and contaminants from metallic scrap is required. Such method should be readily adaptable to be practiced in place in the existing remelt furnaces and preferably eliminate the need for separate delacquering facilities.